(1) Field of the Invention
This invention relates to a process and apparatus for producing ceramic powders, and more particularly to an improved process and apparatus for producing very fine, ultrapure, uniform, spherical, loosely agglomerated ceramic particles.
(2) Description of the Prior Art
The generation of fine, pure, uniform, spherical, loosely agglomerated particles is of intense interest because of their recently recognized properties as suitable starting materials for producing high performance, dense ceramic articles. Densified bodies produced from such powders are predicted to be very strong and to have significantly enhanced property reproducibility. Silicon carbide (SiC) and silicon nitride (Si.sub.3 N.sub.4) are two ceramic materials currently considered highly suitable for use in advanced military and civilian engines.
The direct synthesis of such ceramic powders from gas phase reactants has been achieved using lasers, RF plasma heating systems and heated flow tubes. The first two methods have the advantage over other methods, such as solid phase synthesis and chemical vapor deposition, of avoiding contact of the reactants or products with hot walls (a source of contamination). The latter two methods suffer from non-uniformities in the size of the reaction zone resulting in the production of undesirable wide particle size distribution, agglomeration, etc. The first system is difficult to scale from the laboratory to a production facility.
The use of flame systems to produce ceramic materials has been limited generally to producing oxide powders, such as silicon dioxide (SiO.sub.2) and titanium dioxide (TiO.sub.2) in which the metal containing compound, such as a metal chloride, is added to a hydrocarbon air or hydrogen-air flame, i.e. an already existing flame. A flame system is disclosed in U.S. Pat. No. 4,017,587 to Ditter et al. for the manufacture of amorphous boron carbide by igniting a static gaseous mixture of acetylene and diborane.